Induction coil



April 24, 1951 H. B. M GLADE INDUCTION COIL Filed Dec. 20, 1947 FIG UREFIGURE 2 INVENTOR. WW W Patented Apr. 24, 1951 UNITED STATES PATENTOFFICE INDUCTION 9? Hugh Boyd McGlade, Columbus, Ohio applicationDecember 20, 194}, Serial 793,919

The invention relates to the elimination of induced current, generatedatthe time a normally open "primary circuitof an induction coil is closed.

The induction coil (inductorium) is an apparatus that'generates currentsof induced electricity, and is generally used in the teaching ofphysiology and other allied sciences to induce response in livingmaterial, represented in both Figure l and Figurefiby a resistance 5.

Figure 1 represents a conventional induction coil that will generateinduced current at both the closing and the opening of a normally openprimary switch I.

Figure 2, an improved form of Figure 1, shows the invention in that itwill automatically prevent the induced current from being generated Thehand operated switch I is closed and opened at regular intervals and thestrength of the induced current is gradually increased following eachopening of switch I. The living material, represented by the resistance5, is stimulated by the momentary flow of each effective inducedcurrent, and the resulting single response or contraction is in directproportion to the strength of the current. Since the make current isalways weaker than the following break current, the living materialresponds less to the make than to the following break, with but oneexception: the maximum response of the living material is the same foreither a maximum make current or a maximum break current. No difficultyis encountered in enerating single induced break currents. Singleinduced make currents, however, are diilicult to generate, as indicatedby the following:

When switch I, Figure 1, is closed, the switch contacts frequentlyrebound so that instead of closing only once, they close, open, andclose again in rapid succession. Instead of inducing a single make, theresulting induced current flowing through the resistance 5 i a series ofmakes and breaks (3, 5 or more), immediately following each other. Thesemakes and breaks summ'ate 2 Claims. (o1. 321- -s) and, when eifective,result in a response of the living material (resistance 5) that isgreater than t "at caused bythe' break that follow when w ipli f i ed"In order to eliminate the diificulty encountered at the closing ofsw-itcli I, Figure 1, the com inerical induction coils,used inphysiologylaboratones; are equ pped with a switch a, wiredinparallehwitlfthe' secondary coil 4. To be effective, switch't mustbeclosed before switch I isc'losedaiid opened befor''switchl is opened.Thisp'rocediire is'ehtirely manual and the rapid closing and opening ofthe switches, in the proper sequence, is difficult, and not alwayspositive; even when the control of switch 6 is made automatic with themanual control of switch I. However, since induced current can begenerated only while the strength of the direct current, in the primarycoil 3, changes from zero to maximum (make), or from maximum to zero(break), the problem of automatically preventing induced current frombeing generated at the time switch I is closed, has been solved in thefollowing manner:

The improved induction coil, represented by the schematic diagram inFigure 2, differs from the conventional (Figure l) in that the secondarycircuit is normally open instead of normally closed; and at the timeswitch I is closed, direct current flows not only through the primarycoil 3, but also concurrently through a parallel relay coil I, creatinga magnetic field, in said relay coil I, that closes a normally openrelay switch 8, in series with a secondary coil 4 and the resistance 5.

The closing of switch I changes the strength of the direct current, inthe primary coil 3, from zero to maximum in .002 of a second. Duringthis time, and for an additional .001 of a second, the relay switch 8remains open, due to inherent mechanical delay in closing. Since therelay switch 8 is open at the time switch I is closed, and remains openuntil after the current change takes place in the primary coil 3, it isimpossible for a make current to be induced into the secondary coil 4and flow through the resistance 5.

When the switch I, Figure 2, contacts rebound upon closing, aspreviously described for Figure l, the direct current, flowingconcurrently through the primary coil 3 and the relay coil I, isinterrupted (changes from zero to maximum to zero) every .003 of asecond; each interruption creating a magnetic field in the relay coil I,lasting for .002 of a second. Since the duration of this magnetic fieldis .001 of a sec- 0nd less than the time required to effect a closing ofrelay switch 8, relay switch 8 remains open until after the directcurrent interruptions cease, and a maximum current has been maintainedin the relay coil I, and the primary coil coil 3, for .001 of a second;thus preventing the induction of a series of makes and breaks in Figure2, frequently generated in Figure 1, when switch I rebounds uponclosing.

At the time switch I, Figure 2, is opened, the

relay switch 8 mechanically delays opening for.

.001 of a second. This inherent time delay factor is sufficient topermit the induced break current, picked up by the secondary coil 4, toflow uninterrupted through the resistance 5. The secondary circuit isbroken as soon as the relay switch 8 opens, and the above cycle repeatsautomatically with the next closing and opening of switch I.

I claim:

1. An induction coil comprising a primary coil, a primary switch, and asecondary coil, in combination with a direct current relay comprising arelay coil, and a normally open relay switch; said primary switch beingconnected in series with said primary coil, said relay coil beingconnected in parallel with said primary coil, and said relay switchbeing connected in series with said secondary coil; said relay switchsubsequently closing on the closing of said primary switch, and saidrelay switch subsequently opening on the opening of said primary switch,the secondary coil thus being open to prevent induction on the closingof said primary switch but closed to permit induction on the opening ofsaid primary switch.

2. An induction coil comprising a primary coil, 2. primary switch, asecondary coil, and a normally open secondary switch; said primaryswitch being connected in series with said primary coil, and saidsecondary switch bein connected in series with said secondary coil; saidsecondary switch subsequently and magnetically closing on the closing ofsaid primary switch, and said secondary switch subsequently andmagnetically opening on the opening of said primary switch; saidsecondary switch, open at the time said primary switch is closed,preventing induction, and said .secondary switch, closed at the timesaid primary switch is opened, permitting induction.

HUGH BOYD MCGLADE.

REFERENCES CITED UNITED STATES PATENTS Name Date Koch Mar. 12, 1907Number

